The invention relates to a time division multiplex (TDM) switching network for a telecommunication system or the like having a plurality of switching network units, each of which causes time slots formed on connected TDM lines to be assigned on a space/time-division basis.
The use of this type of switching network unit, which carries out substantially all of the functions of a small TDM central office, is made feasible by its construction according to large-scale integration techniques (LSI). Thus, large switching networks of virtually any size can be built up with only a few types of such switching network units. A network built for a given initial capacity can then be readily expanded to accommodate increased traffic requirements.
According to one design of TDM switching networks, through the use of such switching network units, West German Patent Application No. P 24 44 854.2, a total of three types of switching network units are provided with, respectively, eight, sixteen or twenty-four terminals for TDM lines. Two types of these units are components of a first and a second switching network stage having at least one switching network level. The selection of which of the foregoing units to be used is dependent on the overall size of the switching network.
As long as in such TDM switching networks there are still unwired TDM terminals in the switching network units of the second stage of a switching network level, the switching network can be expanded simply by adding further switching network units in the first stage and by properly connecting the further units through links with the free terminals of the second stage.
If all the TDM line connections of the second stage of a switching network level are wired, further expansion of the switching network is no longer possible without rejumpering existing link arrangements.
In the prior art TDM switching network referred to above, it is not possible to handle the traffic of the TDM lines connected to a switching network unit forming the first switching stage even via another switching network unit. Therefore, the switching network units of the first stage must be designed for a comparatively low number of connections. However, if the two-stage design is to be maintained, this will have as a result that switching network units with relatively greater numbers of terminals in the second stages of the switching network levels must be used.
Since in integrated circuit technology the design costs are of great consequence, it is advantageous to have a single type of switching network unit which forms the basic unit out of which entire switching networks are built on an expandable basis.
Therefore, it is an object of the invention to provide a single type of switching network unit, a plurality of which are used to form a TDM switching network of any desired capacity and which may be expanded to a desired greater capacity through the use of said single type switching network units.